This invention relates primarily to paper pulp refiners and similar rotating equipment in which one or more processing elements rotate with opposed working surfaces in close proximity to other such elements, some of which are mounted and driven for rotation, and others of which are stationary.
In such equipment, the rotor positioning and rotor gap maintenance is critical for optimum performance. A paper pulp refiner may have twin discs, that is a central rotating disc having opposite faces, and opposed non-rotating discs, as shown for example in the Seifert et al. U.S. Pat. No. 4,171,101. However, refiners may employ a single rotary disc or may have a plug-type Jordan refiner elements, as shown for example in Staege U.S. Pat. No. 2,666,368.
Accurate positioning of the rotating member with respect to the non-rotating members is necessary for optimum performance and for control in quality variations. Also, mechanical positioning problems can reduce the life of refining plates. Further, in conventional refiners, the bearings are lubricated with materials that may not be mixed with, and do not tolerate, the process fluid. Therefore, when a bearing seal fails, the refiner also fails, and must be shut down.
The inventors herein previously have addressed the needs of refiner systems and the maintenance of accurate refining gaps and rotor positioning by using magnetic bearings, as disclosed in their U.S. Pat. No. 5,947,394 issued Sep. 7, 1999, and incorporated herein by reference.